The removal of entrained gasses from liquids is an important exercise in a variety of manufacturing and/or analytical processes. An example process in which liquid degassing is widely utilized is in liquid chromatography applications. The presence of dissolved gasses can be undesirable in such applications, wherein the presence of dissolved gasses interferes with the functionality or accuracy of the application.
In the case of liquid chromatography, for example, dissolved gasses in the chromatographic mobile phase can manifest itself in the form of bubbles, which can cause noise and drift in the chromatographic detector. Moreover, the existence of gas bubbles can cause erroneous absorption signatures at the detector.
As chromatographic analyses diversify, applications with relatively high fluid flow rates (>20 ml/min) are becoming more common, especially for separating and purifying compounds from a mixed solution after a synthesis or from natural extracts. Such flow rate in liquid chromatography is known as “preparative scale” liquid chromatography, and normally involves mobile phase (solvent) flow of at least 20 ml/min, and may, in some cases, be between 100-250 ml/min. Analytical scale liquid chromatography, by contrast, typically involves mobile phase flow rates of 0.1-10 ml/min. A variety of degassing solutions are in place for analytical scale HPLC, with the most common utilizing semi-permeable (liquid-impermeable, gas-permeable) tubing in a flow-through arrangement, wherein the solvent mobile phase is driven through the lumen of the tubing within an environment conducive to the removal of gaseous species from the liquid solvent through the tubing wall. Such degassing systems are described in, for example, U.S. Pat. Nos. 3,751,879; 5,340,384; 5,980,742; 6,248,157; and 6,494,938, the contents of which being incorporated herein by reference.
The arrangements described and employed in conventional degassing systems, however, are inadequate to suitably degas the solvent flow rates utilized in preparative scale liquid chromatography. One approach to degassing in high solvent flow rate regimes is to use a plurality of tubular membranes as a hollow fiber bundle in a degassing module, wherein, in some cases, more than 100 hollow fiber separation membranes may be bundled together. Example hollow fiber degassing bundle arrangements are described in U.S. Pat. Nos. 3,339,341; 3,422,008; and 4,351,092. Typically, however, manufacturing of such hollow fiber degassing modules is difficult, particularly in potting the fibers within the housing when the fibers are fabricated from low surface energy materials such as PTFE or Teflon™ AF (which are desired for their membrane properties).
Another approach to liquid degassing in high flow rate regimes is the use of a flat membrane in a degassing module. However, manufacturing such flat degassing membrane modules has proven difficult, both to seal the flat membrane within the module, as well as to manufacture a pin-hole free, uniform flat film.
It is therefore an object of the present invention to provide a degassing module that is both effective in degassing fluids at high flow rates, and is capable of being economically and reproducibly manufactured.